A Two Way Active Measurement Protocol TWAMP is a protocol for measuring two-way or round trip metrics between network devices. In the TWAMP architecture a session-receiver is called a session-reflector and a session-sender is called a session-server. The session-reflector has the capability to time stamp and return a measurement packet when it receives the measurement packet from the session-server. Unlike the session-server, the session-reflector does not collect any packet information. It just time stamp the packet and send it immediate back to the server. The server is an end system that manages one or more TWAMP sessions, and is capable of configuring per-session state in the endpoints. The session-server and the session-reflector exchange test packets according to the TWAMP-test protocol for each active session. In TWAMP, unicast messaging is used to exchange test packets between two TWAMP entities [see “A Two-Way Active Measurement Protocol (TWAMP); RFC 5357]. To be able to verify connection between for example small base stations and a Radio Network Controller, a unicast-based test session server open and provide a test session for each unique user.
FIG. 1 belongs to the prior art and discloses measurement of connectivity between a Radio Network controller RNC 15 (session-server) and small base stations, so called Pico BTSs 16-23 (session-reflectors). The server and the reflectors are connected via routers 25 in a tree structure. The connectivity measuring in FIG. 1 is performed by the Two Way Active Measurement Protocol TWAMP by using unicast. The session-server 15 in the figure manages eight TWAMP test sessions. The session-server and each session-reflector exchange test packets according to the TWAMP measurement architecture for each active session. A unicast message is a message directed to a specific device on a network (just one specific device). Unicast routing is the process of forwarding unicasted traffic from a source to a destination by using routing protocols such as e.g. Routing Information Protocol (RIP). In FIG. 1 can be seen how a first test session 1 comprising three test packets 1a,1b,1c is forwarded from the session-server 15 via the routers 25, to a first session-reflector 16, how a second test session 2 comprising three test packets 2a-2c is transmitted from the session-server 15 to a second session-reflector 16, and so on until all the reflectors 16-23 have received their packets. When a reflector has received a test packet it time stamp's the packet and send it back to the session-server 15. If the number of session-reflectors increases this will result in problems with increasing bandwidth consumption since each of them will have a TWAMP session. A lot of extra measurement traffic is then sent via narrow lines taken bandwidth from the data traffic. A second problem with the TWAMP test according to prior art is that the session-server 15 in uplink simultaneously has to handle many replies from the reflectors at the same time. This consumes processing power from the server's other duties.